ISO/IEC 13818-1 (Information Technology-Generic Coding of moving pictures and associated audio information systems) is an international standard that specifies the coding of one or more elementary streams of audio and video as well as other data into single or multiple streams suitable for storage and transmission. A transport stream (TS) combines one or more programs with one or more independent time bases into a single stream. TS packets are 188 bytes in length. Each TS packet has a 4-byte header with a packet ID (PID) that identifies the type of data contained in the packet. In addition to A/V packets, a TS contains system information tables to demultiplex and present programs. A Program Map Table (PMT) is a table that provides the mappings between the program numbers and the elements that comprise them. It includes a list of PIDs associated with each program.
The Advanced Television Systems Committee (ATSC) has adopted the Simulcrypt architecture for its Conditional Access (CA) system for terrestrial broadcast. In this architecture, each service is transmitted with Entitlement Management Messages (EMMs) and Entitlement Control Messages (ECMs) for a number of different proprietary systems. This way, decoders using different CA systems can decode the service using a common framework for signaling the different entitlement messages. EMMs carry private CA information specifying authorization levels or services of specific decoders, whereas ECMs contain control words for descrambling authorized services. Each service is comprised of audio and video packets. Any one decoder picks out the packets it needs and ignores the others in the stream.
In a Simulcrypt based CA system, a digital audio/video processing system, such as a Digital Television (DTV), parses the PMT and extracts the service and ECM PIDs using a CA system identification (ID) obtained from the CA module. Normally, each CA module supports only one CA system, and therefore has only one CA system ID. The PIDs of the A/V packets and the PIDs of the ECMs carrying the Control Words (CWs) are sent to the CA module, which descrambles programs having proper purchase entitlements.
Extended Conditional Access (XCA) is a copy protection system for providing local protection of audio and video content during transmission and storage in digital home networks. It specifies access and presentation devices to access, convert and display protected content. Removable security devices (converter and terminal cards) are recommended for performing security related functions. In XCA, the descrambling keys are rebundled in an ECM which is protected by a unique local key. The decoder that receives content with local ECMs therefore may need to handle not only the content protected by its own particular CA system, but by XCA as well.
The National Renewable Security Standard (NRSS) provides a means for renewable security to be employed with digital consumer electronics devices such as digital television receivers and digital VCRs. The security functionality is thus separated from navigational devices. When an NRSS security device receives protected content from its host device, it descrambles it, and sends it back to the host device. This link may also need to be protected.
In an ISO/IEC 13818-1 based system, a program may be scrambled in order to provide a Pay TV service. The transport stream carries the programs, the ECMs and the PMTs. The PMT has an entry for each CA system that protects the program. Each entry contains the CA_system_id, the PIDs of the scrambled streams and the PID of the ECMs that contain the keys to descramble the program.
If the receiving device is also a transformation device which can either add an extra CA system, or replace one (for copy protection, for example, like XCA does), then this device needs to output a transport stream where the PMT has an entry for that new CA system. The receiving device may acquire each and every PMT that is present in the original transport stream, process them, add the entry for the extra CA system and then insert the modified PMTs in the output transport bitstream.
The aforementioned process can be very burdensome due in part to the limited processing power of receiving devices. Furthermore, processing complexities increase due to the fact that PMTs may span more than one transport packet. Thus, adding an entry may mean adding a packet, which in turn poses a multiplexing problem, as the bitstream may already be full or the time stamps may need to be adjusted. A method which overcomes these problems is highly desired.